15N CP/MAS studies of the photocycle of [h1,2-15N2]Arg-bR in 0.1 M NaCl at pH=10 revealed the presence of ~wing~ peaks in the spectra of intermediates prepared by illumination at temperatures between -15~C and -90~C. The two peaks appear downfield and upfield from the broad Arg resonance, and are separated by approximately 24 ppm. We have found a strong dependence of the ~wing~ peak size on the trapping temperature. Solid-state NMR studies of light-adapted [e-15N]Lys-bR show that mixtures of photointermediates bR568, N, M, and L in different proportions are trapped in this temperature range. It appears that the ~wing~ peaks are associated with the M-state of bR. The peak intensities indicate a change in 2 of the 14 labeled nitrogen atoms. Selective inversion of the downfield ~wing~ peak by rotor-synchronized CP/DANTE and subsequent spin diffusion resulted in a reduction of the size of both ~wing~ peaks, similar to the change observed in [h1,2-15N2]Arg.HCl.H2O when studied under the same experimental conditions. Thus the two ~wing~ peaks represent nitrogen atoms from a single arginine residue in bR. This indicates that one arginine residue experiences relatively asymmetric interactions in the M intermediate. A possible candidate is Arg82 which is considered to be part of the Schiff base counterion complex, and is probably involved in an extensive H-bonding system. In CP/MAS studies of arginine-containing model compounds the h-15N chemical shifts ranged from 62.0 to 47.8 ppm for the downfield resonance and from 48.4 to 39.6 ppm for the upfield resonance. The biggest separation, found in Arg.HCl.H2O, was 19 ppm. A more extensive study will be required for a meaningful interpretation of the 'wing' peaks in the M state of bR. 2-D correlation spectroscopy on an appropriately 15N, 13C labeled bR may permit the assignment of the arginine residue responsible for the two 'wing' peaks.